Types, Truth, and Expressions Intro to Computer Science CS1510, Section 2 Dr. Sarah Diesburg

What type(s) would we use To represent your:  Weight  Height  Age  Name  Class status (freshman, sophomore, etc)  Gender  If you owe the university money  If you are taking classes this semester

Yesterday’s Lab – Main Concept Review First we looked at the idea of Conditionals and the basic six operators:  Less than: <  Greater than: >  Equal to: == (Not the same as =)  Not equal to: !=  Less than or equal to: <=  Greater than or equal to: >=

Yesterday’s Lab – Main Concept Review The results of a conditional operator is always a Boolean value.  Meaning ???  Either True or False

Boolean Expressions George Boole’s (mid-1800’s) mathematics of logical expressions Boolean expressions (conditions) have a value of True or False Conditions are the basis of choices in a computer, and, hence, are the basis of the appearance of intelligence in them.

What is True, and What is False True: any nonzero number or nonempty object. 1, 100, “hello”, [a,b] False: zero number or empty object. 0, “”,[ ] Special values called “True” and “False”, which are just stand-ins for 1 and 0. However, they print nicely (True or False)

Boolean Expression Every boolean expression has the form:  expression booleanOperator expression The result of evaluating something like the above is just True or False. Evaluating a boolean operation is a binary operation “if (a<b)” has two operands in expression However, remember what constitutes True or False in Python! “If (a)” will evaluate to True if a is non-zero!

Relational Operators Relational Operators have low preference < 3 – 2 (5 + 3) < (3 - 2) 8 < 1 False

Selection Then we looked at how conditionals are applied in selection statements. Selection is how programs make choices, and it is the process of making choices that provides a lot of the power of computing

Python if Statement if boolean expression : suite evaluate the boolean (True or False) if True, execute all statements in the suite

Warning About Indentation Elements of the “suite” must all be indented the same number of spaces/tabs Python only recognizes suites when they are indented the same “distance” You must be careful to get the indentation right to get suites right.

Python Selection, Round 2 if boolean expression: suite1 else: suite2 The process is: evaluate the boolean if True, run suite1 if False, run suite2

Chained Comparisons In python, chained comparisons work just like you would expect in a mathematical expression: Given myInt has the value 5  0 <= myInt <= 5 True  0 10 False

Compound Expressions Logically 0 < X < 3 is actually (0 < X) and (X < 3) Logical Operators (lower case)  and  or  not

Truth Tables

Compound Evaluation Logically 0 < X < 3 is actually (0 < X) and (X < 3) Evaluate using X with a value of 5: (0< X) and (X< 3) Parenthesis first: (True) and (False) Final value: False (Note: parentheses are not necessary in this case.)